Rename starlingextensions.ColoredText to starlingextensions.TextField

I know this seems a little bit crazy now that we have 3 things named
TextField, but it works like this:

No one uses starling.text.TextField

Fathom uses starlingextensions.TextField (or flash.text.TextField if
you're targetting CPP)

starlingextensions uses flash.text.TextField

It's not really that complicated - just pretend that
starling.text.TextField doesn't exist, and if you were OK with Starling
using the same exact naming scheme as AS3's display hierarchy then
everything should be good.

And besides, this is all hidden by Fathom.Text so the end user shouldn't
have to care about this.